In recent years, there have been increasing demands for a larger capacity and a higher rate in information and communication equipment along with development of multimedia. Signals transmitted through interconnection in information equipment or the like are digital signals of required patterns containing burst signals. It is necessary that optical interconnection transmit such signals correctly, as a matter of course. In addition, challenges to be tackled for optical interconnection used in place of electrical interconnection are downsizing the circuit configuration and lowering the power consumption and cost.
FIG. 6 discloses an optical receiving circuit achieving a fine data transmission efficiency with a relatively simple circuit configuration. As shown in FIG. 6, this optical receiving circuit includes: an optical semiconductor detector (hereinafter, referred to as PD (photodiode)) 1 that converts an optical input L into a current signal; a differential amplifier 2 that converts the current to voltages, and outputs a non-inverting voltage V+ and an inverting voltage V−; a peak detector 5 that detects and outputs a peak voltage Vp of a signal of the non-inverting voltage V+ of the differential amplifier 2; a resistor network 4 that generates a non-inverting input voltage V1+ and an inverting input voltage V1− oscillating at an equal amplitude and being 180° out-of-phase with each other, on the basis of the peak voltage Vp, the non-inverting voltage V+, and the inverting voltage V−; and a discriminator 3 that discriminates signals of the non-inverting input voltage V1+ and the inverting input voltage V1− and outputs a rectangular waveform.
Resistors R1, R2, R3, and R4 constituting the resistor network 4 have such a certain relationship that a non-inverting input voltage V1+ and an inverting input voltage V1− whose oscillations cross each other at the middle points of the amplitudes thereof can be generated at respective nodes (a) and (b) in the resistor network 4.
In general, the output of the differential amplifier 2 has such characteristics that the output amplitude thereof varies in accordance with the input. In order to handle a wide range of input, it is common to employ a configuration additionally including a clamping circuit 2a so as to regulate an amplitude voltage in a case of an input equal to or greater than a given level.
However, regulating the amplitude voltage of the differential amplifier 2 by means of the clamping circuit 2a affects, specifically, widens the pulse widths of the non-inverting voltage V+ and the inverting voltage V−. As a result, an output voltage Vo is outputted with its pulse width distorted with respect to the optical input L. This leads to a problem of causing transmission errors.
Accordingly, there is a demand to reduce a distortion of the pulse width of the output voltage Vo with respect to the optical input L, in a case where the pulse widths of output signals of the differential amplifier are widened as a result of regulating the amplitude voltage of the differential amplifier.